1. Field of the Invention
The present invention relates to a recording apparatus, especially a color recording apparatus, and a copying machine equipped with such a recording apparatus.
2. Description of the Prior Art
In recent years, ink jet type full-color recording apparatuses provided with multiple nozzles for respective color components, i.e. cyan, magenta, yellow and black, have found use in computer terminals, copying machines or facsimiles.
FIG. 1 is a sectional view showing the internal structure of a color copying machine as disclosed in Japanese Patent Application Laying-Open No. 196351/1989.
The upper part of the machine in FIG. 1 is composed of a color image scanner portion 1 which reads the image of an original and outputs digital color image data (hereinafter referred to as the scanner portion 1); and a controller portion 2 which is housed in the scanner portion 1, performs various image-processing operations for digital color image data and has processing functions, such as interfacing with external devices.
The controller portion 2 issues operation-related instructions to the scanner portion 1 and a printer portion 3 in accordance with information that has been entered.
The lower part of the machine in FIG. 1 is the printer portion 3 for recording onto a recording paper a color digital image signal outputted by the controller portion 2.
In the scanner portion 1, the image of an original placed on glass plate 17 and pressed by an original cover 11, a projected image from a projector, or a sheet original image supplied by a sheet feed mechanism 12 is read by an exposure lamp 14, a lens 15, and an image sensor 16 (e.g. CCD) capable of reading line images with full-color, that is the original image is read in such a manner that the color of the image is resolved in respective color component of red, green and blue. Then, various image processing operations are performed by the scanner portion 1 and the controller portion 2, and the processed image is recorded by the printer portion 3 onto a recording medium.
The printer portion 3 is in the form of a full-color ink jet printer which uses a recording head of an ink jet recording type as disclosed in U.S. Pat. Nos. 4,723,129 or 4,740,796, namely, a recording head having an electro-thermal converter (heat generator) for an ejection energy generation element as a recording energy generation means.
The above-described two portions are separable from each other, and may of course be disposed apart from each other when connected via an extended connecting cable.
In FIG. 1, a recording medium such as paper, film or the like (hereinafter referred to as the recording paper) is fed from a paper feed cassette 20 which accommodates cut-sheet recording papers (hereinafter referred to as the cut paper(s)) of a small fixed size (A4 to A3 size in this case), or is fed from a rolled paper 29 for recording of a large size (the A2 to A1 size in this case).
A pickup roller 24 is a roller for feeding the cut papers one by one from the paper feed cassette 20. The cut paper fed is conveyed by cut paper delivery rollers 25 to a paper feed first roller 26.
The rolled paper 29 is fed by a rolled paper feed roller 30, cut by a cutter 31 to a fixed length, and conveyed to the paper feed first roller 26.
Similarly, the recording paper inserted manually is carried by a manual feed roller 32 to the paper feed first roller 26.
The pickup roller 24, cut paper delivery rollers 25, rolled paper feed roller 30, paper feed first roller 26, and manual feed roller 32 are driven by a paper feed motor (e.g. a DC servomotor is available) which is not shown, and these rollers can be brought under on-off control at any time by means of an electromagnetic clutch attached to each roller.
Once a printing operation is started by an instruction from the controller portion 2, the recording paper which has been selected and fed through one of the above-mentioned feeding paths is carried to the paper feed first roller 26. Then, a predetermined amount of a paper loop is formed in order to prevent a bias travel of the recording paper. Afterwards, the paper feed first roller 26 is actuated to convey the recording paper to a paper feed second roller 27.
Between the paper feed first roller 26 and the paper feed second roller 27, the recording paper is caused to sag by a predetermined amount to form a buffer so that an accurate paper feeding operation can be performed between these rollers. A buffer amount sensor 33 is a sensor for detecting the amount of the buffer. The constant formation of such a buffer during paper carriage makes it possible to reduce a load to be imposed on a paper delivery roller 28 and the paper feed second roller 27, particularly, during the conveyance of a large-sized recording paper. Hence, the paper can be delivered accurately.
During printing by a recording head 37, a scanning carriage 34 composed of the recording head 37, etc. is caused to perform reciprocating scanning on carriage rails 36 by the action of a scanning motor 35. During scanning on a forward path, an image is printed on the recording paper. During scanning on a backward path, the recording paper is delivered by a predetermined amount by means of the paper delivery roller 28. At this time, the aforementioned driving system is controlled so that a predetermined amount of buffer is ensured by the paper feed motor while the buffer amount is being detected by the buffer amount sensor 33.
The recording paper that has been printed on is discharged onto a copy receiving tray 23, and the printing operation is thus completed.
Next, a detailed description of the surroundings of the scanning carriage 34 will be offered with reference to FIG. 2.
In FIG. 2, a paper delivery motor 40 is a drive source for intermittently delivering the recording paper. This motor drives the paper delivery roller 28, and also drives the paper feed second roller 27 via a paper feed second roller clutch 43.
The scanning motor 35 is a drive source for causing the scanning carriage 34 to scan in the directions of arrows A and B via a scanning belt 42. In this example, pulse motors are used as the paper delivery motor 40 and the scanning motor 35 so that paper delivery can be controlled accurately.
When the recording paper has reached the paper feed second roller 27, the clutch 43 and the paper delivery motor 40 are actuated to convey the recording paper on a platen 39 to the paper delivery roller 28.
The recording paper is detected by a paper sensor 44 provided on the platen 39. The information on its detection is utilized for positional control, jam control, etc.
When the recording paper has reached the paper delivery roller 28, the clutch 43 and the paper delivery motor 40 are turned off. At the same time, a suction operation is performed from inside of the platen 39 by means of a suction motor (not shown) to attract the recording paper onto the platen 39.
Prior to the image recording onto the recording paper, the scanning carriage 34 is moved to the position of a home position sensor 41. Then, forward scanning is carried out in the direction of arrow A. During this action, inks of cyan (C), magenta (M), yellow (Y) and black (BK) are ejected from predetermined positions by the recording heads 37 provided in correspondence to the respective colors, whereby an image is recorded. Upon completion of image recording corresponding to a predetermined length, the scanning carriage 34 is brought to a halt. Backward scanning is begun in the opposite direction, the direction of arrow B, whereby the scanning carriage 34 is returned to the position of the home position sensor 41. During the backward scanning, that amount of the paper corresponding to the length of the paper recorded by the recording heads 37 is delivered in the direction of arrow C by driving the paper delivery roller 28 by means of the paper delivery motor 40.
The recording heads 37 use four ink jet heads corresponding to the above-mentioned respective colors. The reference numeral 49 is a variable resistor which is provided for each recording head and used to set the optimal driving voltage value for each recording head.
By repeating the procedure described above, images are recorded on the entire surface of the recording paper.
In the conventional color copying machine with a multi-nozzle head, as described hereinabove, the original to be copied was read by a sensor, and the resulting signals for red (R), green (G) and blue (B) were converted by using a masking table RAM (random access memory) into signals for respective components, cyan (C), magenta (M), yellow (Y) and black (BK). The converted signals were further binarized to become on-off signals for the respective nozzles so that color copying would be performed.
The foregoing conventional example, however, posed the following problem: If a non-ejecting portion occurred in any of the nozzles of BK head (BK nozzle,) owing to clogging or some other cause, a recording operation was performed as a whole with the defective nozzle failing to eject. As a result, an unrecorded portion was present in a streaky form in the resulting copied image as if a white line were drawn there. Consequently, an image with a poor finish was obtained.